ajax回调函数不执行 请输入长度为10-50-50的问题标

 <%@ page language="java" import="java.util.*" pageEncoding="gbk"%>

<html>
  <head>
  <script type="text/javascript" src="js/jquery-1.7.2.js"></script>
  <script type="text/javascript">
    function checkAccount(){

      var account = $("#account").val();

         $.post("SServlet",{"account":account},function(data){

            alter(data);
            if(data=="true"){
                    $("#s1").val("可以使用");

                }else{
                    $("#s1").val("不能使用");
                    }



         });


        }

   </script> 
  </head>

  <body>
    <input type="text" id="account" onblur="javascript:checkAccount()" name="account"/><span id = "s1"></span>

  </body>
</html>
//***************************************上面的是jsp

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.jsp.JspWriter;

import com.sun.xml.internal.bind.CycleRecoverable.Context;
import com.sxt.dao.UserinfoDAO;

public class SServlet extends HttpServlet {

                //如果要把中文数过去 加这句response.setContentType("text/html;charset=gbk");
    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {

        System.out.println("****");
        request.setCharacterEncoding("utf-8");
        response.setContentType("text/html;charset=gbk");


        String name = request.getParameter("account");
        System.out.println(name);
        UserinfoDAO udao = new UserinfoDAO();
        boolean k = udao.check(name);
        System.out.println(k);
        PrintWriter out = response.getWriter();   //PrintWriter
        out.print(k);




    }

}
//********************************上面的servlet执行正确 

****
大灯
true
//*********************
但是回调函数拿不到值 help me

http://ask.csdn.net/questions/209491